OBJECTIVE to characterize the onset of nucleolar and extranucleolar transcription and expression of the nucleolar protein, fibrillarin, during preimplantation development in macaque embryos developing in vitro. RESULTS Extranucleolar transcription is initiated at the 2-cell stage, and nucleolar transcription and expression of fibrillarin are initiated at the 6- to 8-cell stage in macaque embryos developing in vitro. These results have important implications for understanding normal and impaired gene expression in primate embryos. FUTURE DIRECTIONS We plan to extend these studies, as well as studies involving expression of stage-specific genes, to embryos derived from in vitro matured oocytes and to reconstructed embryos produced by nuclear transfer in order to study impairments in genome activation and nuclear reprogramming. KEY WORDS fibrillarin, macaque, embryo, mRNA, rRNA FUNDING NIH RR00167, NIA AG12179 and HD-22023